The present invention relates in general to a scroll compressor and more particularly to a chock reduction mechanism for reducing a shock at the time of starting of the compressor.
A scroll compressor having a shock reduction mechanism has been used for air conditioners in automotive vehicles. In general, the air conditioner for automobiles is driven by an engine of the automobiles by way of an electromagnetic clutch and a belt so that driving and stop of the air conditioner is selected by an on-off operation of the electromagnetic clutch. Therefore, shocks are added to a body of the automobile due to a load variation at the starting time of the air conditioner and, consequently, a riding comfort is spoiled. Thus, an attempt has been sought to restrict or lessen the load variation at the starting time and to lessen a shock received by the body of the automobile.
An attempt is made to overcome the shortcomings described above by providing a new mechanism for a scroll compressor, as disclosed in JP-A-7-324690 in which the scroll compressor has, on an end plate of a fixed scroll member, a cylinder extending in a radial direction and a bypass channel which connects the cylinder with an operation chamber or a compression space. The cylinder is provided with a spool valve to displace the spool valve within the cylinder by the use of a pressure difference, so that a refrigerant gas which is in the midst of compression at the starting time is returned to a suction chamber through the bypass channel and the cylinder. This permits reduction of volume of the compressor at the starting time and, therefore, the load difference at the starting time can be reduced.
However, the scroll compressor suggested by JP-A-7-324690 involves some problems that a compression load is generated by a compression loss because of utilization of the by-pass channel provided for the purpose of returning the refrigerant gas into the suction chamber and, therefore, a reduction effect of a shock to the vehicle body is limited to a low level. Further, in order to reduce a pressure loss at the by-pass chamber, the size of the spool valve and the cylinder must be designed to be large enough and, accordingly, this results in a large-size fixed scroll member and finally a large scaled entire structure of the scroll compressor. Besides the above, when the discharge pressure which provides a pressure difference for driving the spool valve results in a pressure variation as pulsation or the like, it is likely that the spool valve is driven out of the predetermination. Consequently, there are cases that the reduction effect of shock to the vehicle body is lowered.